Identification

What is in my ceiling?

How to tell what is moving in your Auckland ceiling from the sound, the timing and the droppings, before anyone comes out and before you buy the wrong thing.

The short answer

You can usually identify a ceiling visitor from three things: when the noise happens, what it sounds like, and what the droppings look like. Rats are heard as running and scratching shortly after dark and before dawn. Mice are lighter, more continuous and often audible in a wall rather than overhead. Possums are unmistakably heavier, with thumping and occasional vocalisation. Birds are the only one active in daylight.

Start with the time of night

This single question narrows it faster than anything else. Rats and mice are nocturnal, and activity concentrates in the two or three hours after full dark and again in the hour before dawn. If you are being woken at eleven at night and again at five, that is a rodent.

Possums are also nocturnal but they arrive and leave, so you tend to hear a distinct entry event in the evening and an exit before dawn, rather than continuous movement.

Anything active in daylight is almost certainly a bird, and in Auckland that usually means starlings or sparrows nesting under the eaves or in the roof space. Bird activity peaks in the morning, is noisiest in the nesting season from about September to January, and often includes cheeping.

Then the weight and the character of the sound

A mouse is very light. People describe it as a faint scurrying or a tiny scratching, frequently inside a wall cavity rather than above the ceiling, and it is often close to a kitchen. It is the one most likely to be dismissed as the house settling.

A rat is clearly audible. Running is the giveaway, usually along a defined route so the sound travels in a line across the ceiling and back. Gnawing is common too, a hard rhythmic sound quite unlike scratching, because rodent incisors grow continuously and have to be worn down.

A possum is heavy enough that most people know immediately it is not a rodent. Thumping rather than running, a slow deliberate quality, and sometimes a hissing or coughing vocalisation. Possums also tend to use the same entry point consistently and leave greasy rub marks around it.

Birds produce fluttering, shuffling, scratching in one spot rather than travelling, and vocalisation. Nest material rustling is distinctive once you have heard it.

The droppings settle it

If you can safely get a look in the roof space, droppings give you a definitive answer without needing anyone's opinion.

Mouse: three to six millimetres, thin, dark, pointed at the ends, and scattered widely because mice deposit constantly as they move. A single mouse produces a surprising quantity.

Ship rat: twelve to thirteen millimetres, curved, tapering at both ends, usually in groups along a travel route.

Norway rat: eighteen to twenty millimetres, noticeably thicker, blunt ends, capsule shaped, and usually in concentrated piles rather than spread out. Finding these in a ceiling is unusual, since Norway rats prefer ground level and below.

Possum: fifteen to twenty-five millimetres, cylindrical, often slightly curved, frequently in clusters, and much more variable in colour depending on diet.

Do not handle droppings without gloves and do not sweep them dry, because disturbing accumulated rodent droppings puts particulate into the air you are then breathing.

Why the answer changes what you should do

It is not academic. A mouse in a wall cavity beside a kitchen, a ship rat running the length of a ceiling, and a possum coming in under a roof tile have three different solutions and almost no overlap between them.

Rodents need identification of the entry route and, in most cases, treatment plus exclusion. Possums are a different regulatory and practical matter and are dealt with by exclusion and trapping rather than by pest control products. Birds in a roof space are removed and excluded, and there is a timing question around active nests.

The other reason it matters is that people frequently buy and apply the wrong product, which at best wastes money and at worst creates a bait shy population that is harder for anybody to treat afterwards.

Questions